I've decided to devote today's column to that dreaded Craigslist ad. You know the one I'm talking about.

FOR SALE, it starts off, innocently enough. Drawing you in. Enticing you, the 2 a.m. car shopper, as you browse Craigslist in your underwear. 2008 MAZDASPEED3. Now you're really excited. You pause for a second. You stop chewing your Pringles. "Imagine the possibilities!", you think. Stick shift. 263 horsepower. Hatchback. That cool hood bulge. It's everything you could possibly want. And then you see those dreaded words: OVER $20,000 INVESTED.

The owner then meticulously lists every single part he's ever added to the car, sort of like this:

-CUSTOM HOOPELBARK AIR FILTER-STAINLESS STEEL POOVELFLAUST EXHAUST (sounds like a RACE CAR, or at least a NORMAL CAR with an exhaust leak!!!)-STAGE 4 POWER KIT-STAGE 5 INTERIOR KIT-STAGE 6 EXTERIOR KIT-STAGE 7 LIGHTWEIGHT OWNER'S MANUAL-CUSTOM AARDVARK RACING LOWERING SPRINGS (don't worry, car will clear most road hazards such as toothpicks and leaves)-VERY EXPENSIVE WHEELS THAT ACTUALLY WEIGH MORE THAN THE STOCK ONES BUT I BOUGHT THEM BECAUSE THEY'RE TEAL-LIGHTWEIGHT KEY (I lost the remote and I only have the valet key)-FAMILY OF RARE BRAZILLIAN SPIDERS ADDED TO CRANK CASE TO SUCK OUT THE SLOW

By then, you already know what's coming, but you scroll down to the bottom anyway, just to see it. I know a 2008 MazdaSpeed3 is only worth $13,000, says the seller, talking about those normal ones; the ones that don't have cool racing seats ("Seat belts not currently installed, but I have them in a box somewhere in my basement"). But with all my mods, this one is a STEAL at $29,500.

And then you click away, dejected, knowing that maybe you would've bought this car, if only the seller wasn't currently pushing a 7 on the highly scientific "One to John Hinckley Jr. Scale of Crazy."

And this leads me to the point I'm trying to make today, which is: modifications don't add value to your car. The idea from this column came from Jalopnik reader Thebloody can into Overlanding, who posted an Oppositelock article about a 2004 Land Rover Discovery he found on Craigslist. Now, this was a nice Discovery. It was a clean Discovery. It was a well-modified Discovery, with a lift kit, and a snorkel, and a Kenwood KDC-BT948HD and a Cobra 75WXST, and a Schumacher 1-12S-CA, all of which might be completely made up, for all I know.

It never ceases to amaze me when people try to make the money they dumped into a car back... A car…
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But then the owner made a grievous error: after listing all of his modifications, he then threw out a sixteen thousand dollar asking price, perhaps forgetting that – somewhere, lurking underneath the awesome 1-12S-CA, and the gorgeous KDC-BT948HD, and the excellent 75WXST – there was still a 2004 Land Rover Discovery. And the last time I checked, the going rate on a 2004 Land Rover Discovery was: whatever the guy at the local scrapyard offers ya.

(AUTHOR'S NOTE: Land Rover Discovery fanatics will undoubtedly see this and get incredibly upset. For this, I apologize. In my defense, however, I must say that you will never be able to hunt me down and maim me, because your head gaskets will never last that long. So neener neener neener!)

So anyway, back to the topic at hand, which was… uh… oh, that's right, modifications.

If you're a regular Craigslist browser, you probably see this all the time: guys who think they can get money out of their modifications when the time comes to sell their cars. This is tremendously unlikely, though I admit there is the occasional modification that will get you a few dollars back.

For instance: if you spend $800 on a 1992 Geo Tracker with a torn soft top, and then you modify it with duct tape and string so that it doesn't leak anymore, you might be able to list it on Craigslist and get $900. Of course, you might also be stabbed to death in a robbery attempt gone wrong. So we see here that this strategy doesn't always work perfectly.

But for the most part, modifications – as an investment – are a terrible idea. There are two reasons for this: number one, nobody wants their car set up like you had it. Those teal wheels you bought? The guy at cars and coffee wasn't taking their picture so he could frame it and put it next to his bed. He took the picture so he could show all his buddies back at work that some guy is driving around in a lowered MazdaSpeed3 with wheels that look like they're color-matched to a 1956 Volkswagen Bus.

And the second reason modifications won't get you more money? Because no one has any idea how they were installed, or who installed them. When a seller says "PROFESSIONALLY MODIFIED!!!!" all I can think about is two sweaty guys who have a motor lying around, and a car lying around, and one night, over a series of beers, they decide to do the obvious: rob some guy who's selling a 1992 Geo Tracker on Craigslist.

So sellers, what we've learned today is that modifications won't get you extra money when it's time to sell. Maybe you'll get a couple grand. But the return will be cents on the dollar. In other words: you modified that car for your own benefit, not the next owner's. So don't be ridiculous with your asking price. Even if you have a lightweight owner's manual.

@DougDeMuro is the author of Plays With Cars. He owned an E63 AMG wagon and once tried to evade police at the Tail of the Dragon using a pontoon boat. (It didn't work.) He worked as a manager for Porsche Cars North America before quitting to become a writer, largely because it meant he no longer had to wear pants. Also, he wrote this entire bio himself in the third person.